feat(generate): immutable attributes are create-authoritative on split update bodies

internal/generate/fluent_test.go

@@ -204,3 +204,40 @@ func TestUnit_Generate_FluentTestHelperRebasesTheChain(t *testing.T) {
 		t.Errorf("helper call = %q, want %q", v.Call, want)
 	}
 }
+
+// TestUnit_Generate_ImmutableIsCreateAuthoritative proves an immutable
+// attribute reaches the create body and never a split update body: the
+// endpoint tests' update models declare a fraction of their create fields,
+// and RequiresReplace owns changes to the rest.
+func TestUnit_Generate_ImmutableIsCreateAuthoritative(t *testing.T) {
+	t.Parallel()
+
+	bp := fluentPilot(t)
+	r := &bp.Resources[0]
+	r.Binding.Body.UpdateRequestType = "models.Tags_API_TagUpdate"
+	r.Binding.Body.UpdateConstructorExpr = "models.NewTags_API_TagUpdate()"
+
+	yes := true
+	for i := range r.Schema.Attributes {
+		if r.Schema.Attributes[i].Name == "key" {
+			r.Schema.Attributes[i].Behaviour.Immutable = &yes
+		}
+	}
+
+	v, err := Resource(bp, bp.Resources[0], Options{})
+	if err != nil {
+		t.Fatalf("Resource: %v", err)
+	}
+	if v.Construct.Update == nil {
+		t.Fatal("a split update body must produce an update target")
+	}
+
+	create := strings.Join(v.Construct.Assignments, "\n")
+	update := strings.Join(v.Construct.Update.Assignments, "\n")
+	if !strings.Contains(create, "SetKey(") {
+		t.Errorf("the create body must keep the immutable field:\n%s", create)
+	}
+	if strings.Contains(update, "SetKey(") {
+		t.Errorf("a split update body must omit the immutable field:\n%s", update)
+	}
+}

internal/generate/render.go

@@ -389,7 +389,7 @@
 }
 
 // Resource builds the view for one resource.
 func Resource(bp blueprint.Blueprint, r blueprint.Resource, opts Options) (ResourceView, error) {
 	// One import set per emitted file, since Go rejects an unused import and the
 	// five files need genuinely different sets.
 	var (
@@ -480,7 +480,7 @@
 	// Evidence-derived rules render beside the hand-declared ones: to the framework they
 	// are the same kind of thing, and a reader of ConfigValidators should meet both.
 	conditional, _ := conditionalValidators(r, impResource)
 	v.ConfigValidators = append(cvs, conditional...)
 
 	v.Interfaces = interfaces(r)
 
@@ -1189,7 +1189,16 @@
 			continue
 		}
 
-		if v.Update != nil {
+		// An immutable attribute is create-authoritative: a split update body
+		// frequently cannot carry it at all -- the endpoint tests' update
+		// models declare a fraction of their create fields -- and even where
+		// it could, sending an unchangeable field on update invites the API to
+		// refuse what the plan already forbids. RequiresReplace (driven by the
+		// same Behaviour.Immutable) owns changes; the update body simply omits
+		// the field. The create body below keeps it.
+		immutable := a.Behaviour.Immutable != nil && *a.Behaviour.Immutable
+
+		if v.Update != nil && !immutable {
 			updateCall := a.Wire.Expand
 			if a.Wire.UpdateExpand != nil {
 				updateCall = a.Wire.UpdateExpand

internal/sdkbind/verify.go

@@ -643,7 +643,10 @@ func verifyWireFields(l *Loader, res blueprint.Resource, ok bodyTypesOK, r *Repo
 		if !a.Wire.SkipExpand && a.Wire.Expand != nil && request != "" {
 			checks[request] = "expand"
 		}
-		if !a.Wire.SkipExpand && a.Wire.Expand != nil && update != "" {
+		// An immutable attribute is create-authoritative: the emitter omits it
+		// from a split update body, so the update model owes it nothing.
+		immutable := a.Behaviour.Immutable != nil && *a.Behaviour.Immutable
+		if !a.Wire.SkipExpand && a.Wire.Expand != nil && update != "" && !immutable {
 			checks[update] = "expand (update body)"
 		}
 		if !a.Wire.SkipFlatten && a.Wire.Flatten != nil && response != "" {